1. Field of the Invention
The present invention relates to a medical imaging apparatus, such as a SPECT (Single Photon Emission Computed Tomography) apparatus, an X-ray CT (Computed Tomography) apparatus, and a gamma camera apparatus, in which a patient on a bed is positioned inside an imaging space defined by a view field of a signal detector for collecting imaging signals to be reconstructed into the images by using signal processing.
2. Description of the Background Art
One example of a conventional medical imaging apparatus is a SPECT apparatus which is a type of a gamma camera apparatus in which a gamma camera for detecting gamma rays through a fan beam collimator from a patient is provided around the patient to which an injection containing a radioactive isotope (RI) had been given, and fan beam tomographic image data for reconstructing tomographic images by using signal processings are collected by rotating the gamma camera around the patient for 360.degree.. The gamma camera of such a SPECT apparatus has a two-dimensional detection capability so that multi-slice tomographic images can be obtained from a single 360.degree. rotation of the gamma camera.
An exemplary configuration of such a conventional SPECT apparatus is shown in FIG. 1, where the SPECT apparatus generally comprises: a bed 6 for carrying a lying patient 9 with a head portion 9a supported by a head rest 1; and a frame 4 having a cylindrical bore 5 into which the patient 9 on the bed 6 is positioned by moving in a horizontal X direction, and a gamma camera 2 capable of rotating 360.degree. around a circumference of the cylindrical bore 5 to collect the tomographic image data. The gamma camera 2 has an effective view field vf in the X direction which is narrower than its full width, and is capable of collecting tomographic image data only within this effective view field vf. The collected tomographic image data are subsequently reconstructed into the multi-slice tomographic images by using the signal processings, and the reconstructed tomographic images are displayed on a display device for medical diagnostic use. Here, the tomographic images can cover only those regions of the patient which are located within the effective view field vf of the gamma camera 2.
Such a SPECT apparatus has increasing demands because it is more useful in the diagnosis of a head portion and a heart portion compared with other diagnostic devices.
However, such a conventional SPECT apparatus has been associated with a problem that an accurate positioning of a target region of the patient within the effective view field vf of the gamma camera 2 has been difficult such that a re-positioning of the patient in the cylindrical bore 5 has often been necessary. This is due to the fact that a simple way of ascertain a correct positioning of the patient before the positioning of the patient inside the cylindrical bore 5 has not been available in a conventional SPECT apparatus such that the positioning of the patient has been depending on an experienced guess of an operator which may not necessarily be so reliable. Thus, the operator of a conventional SPECT apparatus has been required to put up with frequent and cumbersome repositioning of the patient.
Moreover, as already mentioned above, the SPECT apparatus is employed mostly for the diagnosis of the head portion of the patient, so that a capability for an easy and accurate positioning of a small and invisible part of the head portion of the patient is an important requirement in view of a maneuverability of the apparatus. For example, as shown in FIG. 2, a cerebellum portion 11 inside the head portion 9a of the patient 9 has been difficult to position accurately within the effective view field vf of the gamma camera 2 by a single patient positioning operation in a conventional SPECT apparatus.
Another example of a conventional medical imaging apparatus is an X-ray CT apparatus which has a typical configuration as shown in FIGS. 3 and 4.
This X-ray CT apparatus generally comprises: a bed 31 for carrying a lying patient 33, including a carrier plate 36 for moving the patient 33 in a horizontal X direction and a height adjustment unit 37 for adjusting a height of the carrier plate 36 in a vertical Z direction; and a frame 32 having a cylindrical bore 38 into which the patient 33 on the bed 31 is positioned by moving the carrier plate 36 in the horizontal X direction, an X-ray imaging unit including an X-ray tube 34 and a detector 35 which are capable of rotating 360.degree. around a circumference of the cylindrical bore 38 to collect the tomographic image data.
As shown in FIG. 4, the X-ray tube 34 and the detector 35 are located at opposing positions on a slicing plane SP, and are rotated together on this slicing place SP around the patient 33 positioned inside the cylindrical bore 38 during the imaging process.
Now, in such a conventional X-ray CT apparatus, the height of the carrier plate 36 is made to be adjustable by means of the height adjustment unit 37 such that the apparatus can be adjusted to a patient of any physical size.
In adjusting the height of the carrier plate 36 by using the height adjustment unit 37, it is necessary to provide a height indicator for indicating a present height of the carrier plate 36 to an operator.
Conventionally, such a height indicator has been provided as shown in FIGS. 5(A) and 5(B). Namely, the height adjustment unit 37 of FIGS. 5(A) and 5(B) comprises: a fixed lower frame 51 fixed to the floor; a movable upper frame 52 on which the carrier table 36 is mounted and which is capable of moving in the vertical Z direction with respect to the fixed lower frame 51 by being driven by a power source (not shown); a scale 53 attached on a side of the fixed lower frame 51 along the vertical Z direction; and a pointer 54 attached on the same side of the movable upper frame 52 along the scale 53 which points a marking on the scale 53 corresponding to the height of the carrier plate 36 which can be read off by the operator.
However, in this configuration of the height adjustment unit 37 of FIGS. 5(A) and 5(B), the scale 53 is located at such a position that the operator has to bend down in order to read off the scale reading correctly, so that the reading operation is cumbersome. Also, in this configuration, a range of the adjustable heights for the carrier plate 36 is limited by a size of the scale 53, so that it has been difficult to lower the carrier plate 36 as low as considered preferable by many operators nowadays.
Alternatively, a height indicator can also be provided as shown in FIGS. 6(A) and 6(B). Namely, the height adjustment unit 37 of FIGS. 6(A) and 6(B) comprises: a base frame 61 fixed to the floor; a movable frame 62 on which the carrier table 36 is mounted and which is capable of moving in the vertical Z direction with respect to the fixed lower frame 61 by being driven by a power source (not shown); a wire 64 suspended from the movable frame 62 in the vertical Z direction; a position detector 65 such as an encoder or a potentiometer which is attached on the wire 64 and measuring a length of the wire 64 corresponding to the height of the carrier plate 36; a drum 66 for rolling up or down the wire 64 as the movable frame 62 is lowered or raised; and a digital indicator using LED for indicating the height of the carrier plate 36 measured by the position detector 65 which is located on a side of the movable frame 62, such that the indication of the height can be read off easily and accurately.
However, in this configuration of the height adjustment unit 37 of FIGS. 6(A) and 6(B), numerous additional electronic components are required, so that the configuration of the height adjustment unit 37 becomes complicated and the apparatus inevitably becomes more expensive.